ROME — The Vatican allowed reporters on Saturday afternoon an unforgettable glimpse inside the Sistine Chapel before the cardinals lock themselves inside and cast their ballots for pope.

The tour began on St. Peter’s Square, where the sun finally shone on the throngs of tourists after days of clouds and rain. A press official led a small group of us up the vast steps to the Apostolic Palace, where the pope resides. We climbed the grand staircase, framed by towering columns.

The chapel is normally lit only by natural light filtering in through the windows, lending an ancient and melancholy air. Saturday, bright lights were strung from the walls so work crews could do their jobs.

It felt almost like a movie set, with the blue sky and red garments in Michelangelo’s “Last Judgment” fairly burning on the wall over the altar.

In the back of the chapel sat two cast-iron stoves — a cylindrical one for burning ballots, and an auxiliary burner for generating chemical-colored smoke to signal the conclave’s progress: white for pope, black for no pope. The winner needs two-thirds, or 77 of 115, ballots.

Shiny copper stovepipes protruding from the top of each stove were welded together into a single pipe, supported by brass scaffolding, and running up out of the window. Back out on the square, a friend pointed out the little stovepipe sticking up from the roof.

Sunday, many of the cardinals are saying Mass at their titular churches in Rome. Cardinal Sean P. O’Malley will be giving his homily in Italian (and a little English) at his church, Santa Maria Della Vittoria. A spokesman for O’Malley said he spent Saturday in meetings, preparing his homily and having dinner with friends.

The Vatican just released a conclave schedule for the English-speaking press. The action will begin at 4:30 p.m. local time (11:30 a.m. Boston time) on Tuesday, when the cardinals process from the Pauline Chapel to the Sistine Chapel. At 4:45 p.m., each cardinal will swear an oath of secrecy, and the voting may begin.

Assuming no pope is elected on the first ballot, the cardinals will hold a 15-minute vespers service in the chapel at 7:15 p.m. and then return to the Vatican hotel where they are staying during the conclave, Sanctae Marthae, to eat dinner and sleep. They are not allowed access to the outside world during the conclave, which is meant to ensure the integrity and independence of the vote.

In the days following, the cardinals will have breakfast between 6:30 and 7:30 a.m., celebrate Mass in the Pauline Chapel, and then at 9:30 a.m. return to the Sistine Chapel to pray and vote. They take a lengthy lunch break from 12:30 to 4:30 p.m., then begin a second round of voting before breaking for the night at 7:30 p.m.